A lithium secondary battery that comprises a nonaqueous electrolyte and utilizes the transfer of lithium ions between a positive electrode and a negative electrode for charge and discharge of the battery has recently been used as one of new type high output and high energy density batteries.
A lithium secondary battery using a material which forms an alloy with lithium as a negative electrode active material is known. However, it is also known that an active material which forms an alloy with lithium increases and decreases in volume when lithium ions are occluded and released, and the active material is pulverized during charge and discharge cycles and separates from the current collector. This causes deterioration of current collecting characteristics (current collectability) and of charge and discharge cycle characteristics.
A negative electrode for a lithium secondary battery in which an active material layer comprising a silicon material and a binder is formed on a current collector comprising an electrically-conductive metal foil and is sintered on the current collector under a non-oxidizing atmosphere has been proposed (Japanese Patent application No. 2000-401501). The negative electrode provides excellent charge and discharge cycle characteristics.
It has also been found that when a thin amorphous or micro crystalline silicon film which is provided on a current collector comprising an electrically-conductive metal foil by sputtering method or CVD method is used as a negative electrode active material, excellent charge and discharge cycle characteristics are obtained (International Publication No. 01/31720).
However, a negative electrode increases and decreases in volume when an active material occludes and releases lithium ions, cracks occur in the active material layer, and contact resistance in the active material layer increases. This causes deterioration of current collecting characteristics (current collectability) and of charge and discharge cycle characteristics.